The present invention relates to a negative-working photosensitive mixture which contains a diazonium salt condensation product, a polymerizable compound, a photoinitiator and a binder. The present invention further relates to a recording material that is prepared using this mixture and is preferably employed for the production of lithographic printing plates.
Combinations of photopolymerizable mixtures with negative-working diazo compounds, in particular diazonium salt polycondensation products, are disclosed in German Offenlegungsschriften No. 2,361,931 (corresponding to U.S. Pat. No. 4,289,838), No. 2,903,270 (corresponding to U.S. Pat. No. 4,171,974) and No. 3,007,212 (corresponding to British Patent Specification No. 2,044,788). In these combinations, either the diazo compound itself acts as the photoinitiator for the polymerization of the monomer, or an additional photoinitiator is used. The primary advantages offered by these combinations is said to be a better resolution of the copies, as compared with merely photopolymerizable layers, and increased print runs, as compared with layers which exclusively contain diazo compounds as the photosensitive substances. In certain cases it is also possible to perform development with aqueous solutions or even with pure water.
A similar mixture, which contains a binder with cross-linkable allyl side groups, is described in European Patent Application No. 0,104,863.
The diazonium salt polycondensation products disclosed in the above-mentioned publications are compounds prepared by condensing diphenylamine-4-diazonium salts with formaldehyde, optionally followed by a modification of the diazonium salt anion.
These known combinations, some of which contain water-soluble polymers, are often sensitive to unfavorable climatic changes, such as increased temperatures or relative humidity, which in most cases leads to reduced shelf lives. Moreover, the adhesion to a support of layers comprising the known combinations frequently is not optimal, in particular in the exposed state.
U.S. Pat. No. 3,867,147 discloses diazonium salt polycondensation products, which in addition to diazonium salt units contain other units which are free from diazonium groups and are linked with each other and with the diazonium salt units by bivalent linking members derived from active carbonyl compounds, in particular methylene groups. These polycondensation products can be combined with binders to provide printing plates displaying a higher sensitivity to light and lower sensitivity to humidity than the formaldehyde condensation products mentioned above.